Wireline and wireless Internet Protocol (IP) networks have traditionally supported a best effort delivery of all traffic. However, current networks are optimized for real-time voice services, despite the growing need for data services. Furthermore, the constraints imposed by voice and data traffic on the system are quite different. Voice transmissions must be in real time and are intolerant to delays. Large delays in the transmission of voice packets significantly reduce the quality of the voice link. Also, network Grade of Service (GoS) requirements, such as probability of call blocking or outage and area reliability, as well as the treatment offered to all mobile voice users is the same. On the other hand, many data applications are tolerant to reasonable delays without significantly impacting the link and application quality. Thus, quality of service requirements and the treatment required by different data applications are dissimilar.
To support enhanced services, multiple types, or classes, of services have been established and assigned certain quality of service (QoS) parameters that manage queues for each service type. The QoS parameters include delay, jitter, error rates, and throughput. The QoS parameters can be provisioned on a per Internet Protocol (IP) connection or per flow basis through mechanisms such as resource reservation protocol (RSVP) or can be provisioned on aggregate flow, which is classified into service classes. Internet service providers (ISPs) can utilize the service classes, their associated QoS behavior, and QoS provisioning to provide multiple service offerings to their business and consumer customers.
As newer classes of services, with differing QoS requirements and different transmission characteristics are offered, it becomes imperative for wireless carriers to find new methods and techniques to optimally utilize limited air-bandwidth without affecting the overall network GoS. One attempt to ensure continual coverage, and thereby maintain QoS, is the “soft handoff.” In modern wireless networks, Code-Division Multiple Access (CDMA) technology is used to shares frequency across multiple users and applications. CDMA supports a soft handoff, in which a mobile user is communicating with a mobile switching center via two or more cellular antennae sites and the user data is broadcast by all sites to the mobile user. This mode of communication makes the mobile-to-cell link resilient to obstructions in the beam path that can cause the active call to terminate abruptly. For the mobile to drop a call, the paths to all of the cells would have to be obstructed. A greater number of active links between the mobile and the network lowers the probability of dropping a call.
But, a mobile unit in soft handoff will cause all sites in handoff to transmit over a forward link to the mobile unit. This forward transmission from multiple sites to a single mobile unit, while improving the communication link to that particular mobile unit, increases the overall interference for other active mobile units in the system and can potentially degrade the performance of the forward link for all mobile units. Also, as the total forward power is limited, the available power for new users is considerably reduced. If several mobile units are in soft handoff at the same time, this can potentially lead to severe degradation in the overall system capacity.